Now, we head overseas to the red-hot standoff between Russia and the United States. Russia is mobilizing tens of thousands of troops. And the U.S. Circling the wagons with other world powers. Once known as the group of eight. Now known as the group of seven, g-7, because Russia has been exiled. ABC's chief white house correspondent, Jonathan Karl. Reporter: President Obama held an emergency meeting with world leaders today to turn the heat up on Russia, the Russian military ominously added to their forces on Ukraine's border. There's now 30,000 Russian forces there. 10,000 added just over the past week. And nato's U.S. Commander warns, they could invade at any time. Seizing not just eastern Ukraine, but Moldova. The force at the europe/ukrainian border now, to the east, is very, very sizable. And very, very ready. Reporter: Today, president Obama, here to discuss preventing nuclear terrorism, pledged to stand with Ukraine. Europe and America are united in our support of the Ukrainian government and the Ukrainian people. Reporter: And tonight, Russia has been suspended from the elite group of eight top world powers. Now, it's the group of seven, no Russia anymore. Vladimir Putin says his troops on the ukraiyukrainiian border are there for military exercises and nothing more. But officials don't believe that. One official put it, we have every reason to be kept kl

This transcript has been automatically generated and may not be 100% accurate.

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